Abstract: The present invention relates to a process for the preparation of exomethylene cephams, which are useful intermediates in the production of many useful .beta.-lactam antibiotics.More particularly there is provided a process for preparing a compound of formula I ##STR1## wherein n is O or 1, R.sub.1 is hydrogen atom or an organic residue and R.sub.2 is a carboxy protecting group, which process comprises reacting a compound of the formula II ##STR2## wherein X is halogen atom or acetoxy group and R.sub.1 n and R.sub.2 are as defined above with a lanthanide complex.

Abstract: The invention relates to a process for the preparation of a new crystalline monohydrate of 1-(3', 4'-diethoxy-benzyl-6, 7-diethoxy-3,4-dihydro-isoquinolinium-theophylline-7-acetate and if desired of pure 1-(3', 4'-diethoxy-benzyl)-6,7-diethoxy-3, 4-dihydro-isoquinolinium-theophylline-7-acetate free of contaminating oxidation products which comprises reacting 1-(3',4'-diethoxy-benzyl)-6,7-diethoxy-3,4-dihydro-isoquinolinium with theophylline-7-acetate acid in the presence of water and one or more organic solvent(s) and if desired dehydrating the 1-(3',4'-diethoxy-benzyl) 6,7-diethoxy-3,4-dihydro-isoquinolinium-theophyl line-7-acetate-monohydrate thus obtained.